Currently, video play and video telephony are used extensively on mobile terminals. To display a high-resolution video source on a low-resolution liquid crystal display (LCD), a process of scaling down the video source is generally required. On the contrary, to display a low-resolution video source on a high-resolution LCD, a process of scaling up the video source is required.
The source video is scaled by a scaling engine integrated in the display controller. FIG. 1 shows a structure of a display controller in the prior art. As shown in FIG. 1, the display controller 120 is synchronized with the display frame rate, and reads the source video image and other image layers from the system memory 110. The display controller 120 integrates a video channel 121, a rotating module 122, a scaling engine module 123, and a YUV-RGB converting module 124. The display controller 120 rotates the source video image, scales the source video image, and converts the pixel format of the source video image in real time (optional). The overlay processing module 125 overlays the processed video image with other image layers for displaying, and then sends the overlaid image to the LCD 130 for displaying. According to the foregoing structure, the scaling engine module 123 is integrated into the display controller 120 to scale the source video image in real time.
In the prior art, the transient bandwidths required for reading the source video image linearly increase along with the scaling ratio. The transient bandwidths needed by the system memory to read the source video image under scaling conditions=transient bandwidths needed by the system memory to read the source video image in case of no scaling*vertical scaling ratio*horizontal scaling ratio. Table 1 lists maximum input video resolutions that can be supported by the scaling engine of the display controller supplied by a renowned application processor supplier under various LCD resolutions. As shown in Table 1, the vertical and horizontal scaling ratios supported by the display controller are 2 at most.
TABLE 1Maximum Input Image ResolutionPixelClockInterpolation in 3-tap modeInterpolationFrequencyRGB16/YUV422.in 5-tap modeLCD Resolution(MHz)RGB24RGB16/YUV422RGB24QCIF(176 × 144)2354 × 288Not supportedNot supportedCIF(354 × 288)8768 × 576768 × 576768 × 576QVGA(320 × 240)6640 × 480768 × 576768 × 576HVGA(480 × 320)12768 × 576768 × 576768 × 576VGA(640 × 480)241280 × 960 768 × 576768 × 576SVGA(800 × 600)371536 × 1152768 × 576768 × 576XVGA(1024 × 768)611536 × 1152768 × 576768 × 576
During the implementation of the present invention, the inventor discovers at least the following weaknesses in the prior art: The source video image cannot be scaled within a high ratio range in online mode.